Over the last century, mankind has developed a growing understanding of the nature of light. This growing understanding has led to an increasing ability to harness and control light, which has in turn led to improvements in a wide variety of different technologies. For instance, the ability to control photons has led to improvements in communications, such as through the development of fiber optics; improvements in opto-electronics, such as through the development of photo-voltaic cells; as well as the development of near-field optics, a field of study dedicated to the utilization of near-field light, which is the light created around the periphery of an object emitting or being illuminated by light. The study of near-field light has brought about the development of and continuing improvements to many optical devices including many different types of imaging devices as well as optical scanners, filters, switches, modulators, and the like.
Surface plasmon polaritons (also referred to throughout this disclosure as simply plasmons or SPP) exist when light couples with surface plasmons, which are collective electronic excitations running as longitudinal density fluctuations at the interface of a metal (or metallic material) with an adjacent dielectric material. The SPPs thus created can propagate across the metallic material and their energy can then be utilized, for instance via reradiation of the impinged light. Surface plasmons have been generated to advantage on metallic thin films having thickness on the order of tens of nanometers as well as on metallic nanoparticles and metallic nanoshells.
Utilization of plasmons has been seen in many varied applications including label-free monitoring of biomolecular interactions, enhanced DNA hybridization, single-molecule fluorescence imaging, two-photon excitation, molecular sensing, photonic transportation, and high-density nanolithography. For example, SPPs have proven quite useful in sensing technologies such as near-field scanning optical microscopy (NSOM). Traditional NSOM methods couple evanescent photons reflected, fluoresced, or otherwise contacted with a sample with surface plasmons generated on the tip of a near-field probe via location of the probe tip within the penetration depth of the evanescent waves (e.g., about 100 nm). This coupling can enhance and convert the evanescent photons to propagating photons that can then be collected and imaged using far-field optics.
Problems exist with known devices and methods, however. For example, the metallic thin films, nanoparticles, nanoshells, etc. used to generate the plasmon propagation can be difficult and expensive to prepare, but due to the internal damping effect common to such materials and subsequent energy attenuation with increased thickness, materials of such dimensions have been considered to be required in order to attain plasmon propagation. Other problems exist with these materials as well. For instance, heat generated at the metal can cause problems during use, including damage or destruction of samples being examined. In addition, and in particular during NSOM processes, the close proximity between the probe tip and the sample that is necessary to ensure photon-plasmon coupling can create shadow effects that can then detrimentally effect the imaging of the sample.
What is needed in the art are additional materials that can support surface plasmons to generate SPPs and methods for developing such materials to form optical devices.